I love the shadowing. The T-shirts in the boys are similar and present a more solid package (?). The T-shirts in the girls have greater variety and do not blend together as well. I do not see this as a mistake or error on your part. They just are not playing nice with one another.
This is all I could see that might be causing you to think there was a mistake or problem. Remember, they are her shirts and she will love it.